Help again please. Father Frank & Bigshrimpin

[gofastsandman]

`89 20 sf w a 96 ocean pro 150 w/ a mich. 14 1/5 x 17 prop.
Well it now pulls 5500 w 3 ppl and 50 gals at 39 mph on a 2 way pass gps after 100 hrs of new use in the last 4 mos.
Here`s the confusion/ ignorance.

Merc`s online prop selector for a mirage plus for light load
is 15.250 x 19 ,a good load is 15.380 x 18.

Does the difference in design allow for more diameter and pitch?

I have only about 3/4" - 1" of clearance to the vent plate.
Is that also a concern?

Thanks to all
GFS